1. Technical Field
This disclosure relates to a liquid crystal display device that displays an image on a liquid crystal display unit.
2. Description of the Related Art
A liquid crystal display device is used as a high-definition color monitor of a computer or another information apparatus, or a display device of a television receiver. Basically, the liquid crystal display device includes a liquid crystal display unit in which liquid crystal is held between two substrates, at least one of which is made of transparent glass or the like. The liquid crystal display device includes a drive unit that selectively applies a voltage to various electrodes for pixel formation formed on the substrates of the liquid crystal display unit. The liquid crystal display device performs lighting and extinguishing of predetermined pixels according to the voltage application by the drive unit. The liquid crystal display device is excellent in contrast performance and high-speed display performance.
In general, the liquid crystal display unit includes a plurality of gate signal lines, a plurality of source signal lines, and a plurality of pixels. Each of the plurality of gate signal lines is provided to extend in the lateral direction (a main scanning direction) for example, and provided side by side in the longitudinal direction (a sub-scanning direction). Each of the plurality of source signal lines are provided to extend in the longitudinal direction (the sub-scanning direction) for example, and provided side by side in the lateral direction (the main scanning direction). A plurality of thin film transistors (TFTs) and a plurality of pixels are arranged in a matrix at crossing points of the plurality of gate signal lines and the plurality of source signal lines.
The drive unit applies a voltage for turning on and off the TFTs to the gate signal lines. The drive unit applies a voltage based on an image signal to the source signal lines to change the transmittance of the liquid crystal to a value corresponding to the applied voltage. At this point, the drive unit retains the image signal for one horizontal period and outputs the image signal to the source signal lines of the liquid crystal display unit. As shown in FIG. 18, the source signal line of the liquid crystal display unit is represented by an equivalent circuit including a wiring resistor, a gate capacitor of the TFT, a capacitor between wiring layers, and a capacitor between the wiring layer and another liquid crystal layer. Therefore, when an input image signal changes for each one horizontal period, charging and discharging for the capacitors are repeated. Thus, a current amount supplied from the drive unit increases, whereby the temperature of the drive unit rises. When the temperature of the drive unit exceeds a guarantee temperature for guaranteeing the operation of the drive unit, this leads to deterioration in characteristics of the drive unit. Therefore, in a technique described in Japanese Patent Application Publication No. 2011-164288 for example, it is detected whether the temperature of a chip constituting the drive unit rises to temperature equal to or higher than a predetermined temperature and a maximum output voltage of a gamma correction voltage is reduced on the basis of a detection result, whereby the amplitude of an applied voltage from the drive unit to pixels is reduced.
As it is seen from FIG. 18, when the input image signal does not change for each one horizontal period, since charging and discharging for the capacitors are not performed, the temperature of the drive unit does not rise. In other words, when the application of the maximum output voltage of the gamma correction voltage is continued, it is unnecessary to reduce the amplitude. However, in the technique described in above-mentioned Japanese Patent Application Publication No. 2011-164288, the maximum output voltage of the gamma correction voltage is reduced irrespective of a change in the input image signal. Therefore, even when it is unnecessary to reduce the amplitude, the amplitude of the applied voltage from the drive unit to the pixels is reduced. Therefore, in the technique described in above-mentioned Japanese Patent Application Publication No. 2011-164288, it is difficult to suitably control the amplitude of the applied voltage from the drive unit to the pixels according to the change in the input image signal.